ios xcode cannot run using the selected device

xcode4.2 在运行是系统提示：ios xcode cannot run using the selected device

map程序，在viewDidLoad方法中直接赋值经纬度：

BMKCoordinateRegion region;
region.center.latitude = 45.58008;
region.center.longtude = xxxxx;
region.span.latitudeDelta = 0.2;
region.span.longitudeDelta = 0.2;
if(_mapView){
    _mapView.region = region;
    //NSLog(@"%f,%f",);
}

选中工程修改：summary->Deployment Target->4.3(默认为5.0)

修改后运行不再出现上面的提示。